Method and machine for locating variations in tension in a saw blade

ABSTRACT

A method and machine for hammering circular saw blades automatically, to correct uneven distributions of residual stresses, and distortions of the blade surfaces from true planes, so that the blades will run true. This operation has previously only been performed manually, by highly-skilled craftsmen. The saw blade is elastically deflected so that its normally-planar surface lies in a curved surface of a predetermined contour. A proximity sensor passes over the blade to detect deviations of its surface from the predetermined contour, which occur at points of uneven stress distribution or surface distortion. At such points, the blade is arrested and hammered until the fault is corrected.

This is a division, of application Ser. No. 555,155, filed Mar. 4, 1975now Pat. No. 3,964,348.

BACKGROUND OF THE INVENTION

This invention relates to saw straightening and tensioning and, morespecifically, to a novel machine and method for automatically correctingsurface defects in a circular saw blade and providing the proper tensiondistribution to permit the blade to run straight and true at cuttingspeeds.

Toward the beginning of the 19th century, the circular saw was startingto come into use, revolutionizing wood cutting methods. The speed withwhich the "buzz saw" was able to cut lumber was totally unheard of andunimaginable, and this new tool was generally considered miraculous. Yetin the beginning the circular saw was far inferior to modern saws in itsability to cut straight and true.

Although manufactured to the best possible tolerances, it was found thatwhen a circular saw was operated at the high rate of rotation necessaryfor cutting wood, the outer edge of the saw blade had a tendency todeviate from the cutting line either to one side or the other, or toboth sides, producing a somewhat wavy cut. There was also a tendency forthe edge to start the cut off to one side or the other of the intendedline, in which case the blade would tend to lead the cut in thatdirection. Yet when the saw blade was stopped, it was found to be asstraight and true as before.

Eventually it was learned that the invisible defects which resulted inuneven cutting included both minute surface deformities, and improperdistribution of residual tension stress in the saw. Substantial tensionstress is induced in the blade by centrifugal force when it is rotatedat the high angular velocities necessary for cutting wood and othermaterials. To this tension is added or subtracted the residual stressesin the blade, so that non-uniformity of tension distribution producesuneven strain. Irregularities in the blade surface also interfere withtrue running as the tension changes when cutting speed is approached.Thus the blade may be deflected from running true by either of thesetypes of defects.

Areas on the surfaces of the blade at which residual tension stressessignificantly vary from the normal level of tension in that portion ofthe blade are commonly referred to as "tight" or "loose" spots. Commongeometric deformities include bulges, ridges, kinks and twists.

For many years, the problem of poor tension distribution and invisiblesurface defects was unrecognized and unsolved. The quality of a circularsaw blade and its ability to cut straight and true was largely a matterof chance.

Ultimately it was learned that the operation of a circular saw could beimproved by performing certain hammering operations on the saw blade.But it was found that no particular hammering method would improve theoperation of all blades, and that varying types of hammering proceduresmust be utilized to correct different defects. The proper hammering ofsaws soon became recognized as a highly-skilled craft, an art requiringintuitive analysis of problems and the development of often-uniquesolutions. There developed a highly-skilled craftsman, the sawsmith, whohas since that time been one of the highest paid representatives of allthe shop trades. Because of the great skill required, the number ofsawsmiths practicing this trade has remained greatly limited and thecraft has often been practiced in secret, increasing the aura ofmysticism surrounding this function. The sawsmith utilizes a collectionof carefully-selected hammers, straight edges, and other tools, as wellas senses trained by long experience, to inspect a saw blade forimperfections, mark them as to type and location, and employ the properhammering patterns and tools to remove these imperfections from the saw.Proper hammering over both surfaces of the saw blade produces a moreuniform tension distribution and removes surface flaws, enabling the sawto run straight and true at cutting speed.

While all circular saws are benefited by such hammering, omission of theprocedure leaves more pronounced running defects in large circular sawsthan in small ones, in proportion to mass and diameter. Coupled with thehigh rate of pay and shortage of sawsmiths, this has dissuadedmanufacturers from hammering small circular saw blades, such as thoseused by the home handyman. If hammered at all, they are only givencursory treatment in an effort to produce a predicted tensioning. Thus,economic pressures have resulted in the marketing of inferior circularsaw blades. But the cost of hammering by a sawsmith might in some casesexceed the cost of the saw itself.

In the nearly 200 years of history of the circular saw, manyimprovements have been made in blades and in methods for theirmanufacture and treatment. But after the development of the sawsmiths'craft, no further substantial advancement was made in this mostdifficult and expensive aspect of the treatment of circular saw blades.

The exercise of the sawsmiths' art involves "dishing" the blade, thatis, elastically warping or bending it around an axis parallel to itsdiameter, so that its surface takes the form of a curved cylindricalsegment. The sawsmith then applies a straight edge to the blade surfacesat right angles to their curvature, which reveals to a practiced eye thenature and location of defects in the saw. Each defect is marked in aspecial way which points out, upon later examination, just what typeeach defect is, so that one may select the tools and techniques bestsuited for its correction. The sawsmith then places the saw on an anviland commences hammering the marked areas, guided only by his marks, andhe must be extremely careful to hammer in the proper manner and in thecorrect location. While this rectifying operation is being performed,the sawsmith may also hammer generally over the whole surface of the sawto obtain an overall distribution of tension appropriate to that type ofblade.

When the sawsmith applies his straight edge, he is actually findingbulges and depressions representing either physical distortions, or"tight" and "loose" spots on the surface of the saw. The latter areareas of substantially greater or lesser residual tension stress thanexists in the surrounding surface. When the saw is dished, any tightspots on the blade surface tend to bulge inwardly from the concavesurface, being drawn out as a chord spanning a portion of this surface,while loose spots tend to bulge outwardly. When the blade is laid flat,these areas generally cannot be detected. Kinks, ridges, and otherphysical distortions inadvertently produced on the saw blade can also bedetected by the way they stand up under the straight edge. Additionally,the manner in which the saw curves when dished is, to the skilled handand eye of the sawsmith, a measure of overall tension distribution inthe saw.

BRIEF DESCRIPTION OF THE INVENTION

The general objects of this invention are to rectify defects in sawblades without the services of skilled craftsmen; and to reduce theexpense and time required for producing properly-tensioned saw blades.The invention provides a new method and an automatic machine forcorrecting defects in saw blades by hammering. What has been ahighly-skilled, almost mystical craft may now be performed automaticallyby a machine and a virtually unskilled operator.

According to a preferred practice of the invention, a saw blade to behammered is mounted on a carriage, and elastically deflected so that itssurface generally coincides with a curved surface having a predeterminedcontour, to which the blade surface would fully conform if correctlystraightened and tensioned. Preferably, the blade is deflected about anaxis parallel to its diameter to lie in a curved plane, that is, asegment of a cylinder generated by a straight line moving parallel to arectilinear axis in a curved path. Alternatively, the blade may bedeflected to lie in the locus of a segment of the surface of a curvedgeometric solid, such as an oblate spheroid or ellipsoid, for example.The blade is caused to rotate about its center, but the deflecting meansremain stationary, holding the surface of curvature of the blade in thesame position; the blade flexes as it rotates to accommodate thiscondition.

A proximity sensor is positioned at an operating station a predetermineddistance from the concave side of the curved surface of the deflectedblade. A relative reciprocating or oscillating motion is created betweenthe sensor and the carriage bearing the blade, so that the sensor sweepsthrough a helical path with respect to the surface of the rotatingblade. The carriage may be mounted to oscillate on a pair of tiltedaxes, or other arrangements may be made, to cause the distance betweenthe sensor and the locus of curvature of the surface of the blade toremain substantially constant throughout this motion.

The sensor continuously monitors its distance from the concave side ofthe blade surface. A tight spot, at which the residual tension isexcessive, will form a chord lying inside the curve of this area. At anypoint where the distance to the blade surface is found to be less thanthe predetermined value, indicating the presence of either a tight spotor a physical deformity, the rotation of the blade and the relativemotion of the carriage are immediately stopped. The sensor is withdrawnfrom its position over the saw blade, the blade is released from itsdeflected form so that it flattens out to lower the detected defectiveregion onto an anvil, and a hammer is caused to strike this region. Thehammer is then raised and the sensor returned to its operating positionover the blade. After the saw has once again been deflected into itscurved configuration, if the distance from the sensor to the defectivearea of the saw blade is found to have been corrected by the hammerblow, relative motion of the blade and carriage is resumed. If the flawhas not, however, been fully corrected, the blade and carriage remainstationary, the sensor is withdrawn, and the hammer again strikes thedefect. This action continues until the defect has been corrected.

By examining and treating both surfaces of the saw blade in this way,substantially all significant defects can be swiftly and accuratelyrepaired, eliminating the slow, laborious examination, marking ofdefects, and hammering which previously had to be performed manually byan expert sawsmith.

It will be observed from the foregoing that the principle on which thisinvention operates is that defects in a saw blade surface can bedetected by locating local displacements from a predetermined curvedsurface into which the blade is elastically warped, or by detectinglocal variations in the distance from a parallel curved surfaceuniformly spaced away from the predetermined surface. The features ofthe improved method may be summarized, and contrasted withpreviously-known methods, by the following:

1. As opposed to bending the blade with a random degree of curvature, Ibend it into a predetermined, predictably-curved surface.

2. In place of bending the blade about only one axis, or at most severalaxes, I rotate it continuously while retaining the surface of itscurvature in a fixed location, thereby subjecting the body of the bladeand any defective areas to flexure successively about every diameter.This improves the reliability of discovery of defects, many of which maybe asymmetrical and therefore show up more prominently when bent aboutone diametral axis than another.

3. Instead of detecting defects by placing a straight edge parallel tothe axis of curvature in an attempt to identify at one time alldeviations from rectilinearity along the full length of a chord of theblade surface, I employ a sensor which individually checks only a smallsurface area at a time, thus avoiding the introduction of ambiguity bythe mutual interplay of various defects in a large-area sample.

4. As opposed to marking the discovered defects in a separate operationand hammering them later, I obviate the need for the marking step byhalting and relaxing the blade immediately upon detecting each defect,and correct it by hammering then and there.

5. Instead of undertaking to correct saw blades by a purely-manualguesswork method, I perform the detection and correction operations withmuch more reliable, as well as more rapid, automatic or semiautomaticmeans. Where such low production rates are desired that the cost of anautomatic machine is not justified, my method may be performed with theuse of at least partially manually-operated equipment conforming to theinvention, with an improvement in the uniformity of results, and withcomparatively-unskilled labor.

DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outthe subject matter which I regard as my invention, it is believed that aclearer understanding may be gained from the following description ofpreferred embodiments thereof, referring to the accompanying drawings,in which:

FIG. 1 is a diagrammatic isometric view of a deflected circular sawblade;

FIG. 2 is a diagrammatic perspective view showing the deflected sawblade of FIG. 1 turned through an angle of 90°;

FIG. 3 is a plan view of a circular saw blade, showing exaggeratedsurface defects marked thereon;

FIG. 4 is a diagrammatic cross-sectional view taken substantially alongthe line 4--4 of FIG. 3, illustrating the behavior of a surface defectof a deflected saw blade;

FIGS. 5 and 6 are diagrammatic cross-sectional views of circular sawblades, illustrating the effects of overall tension distribution;

FIG. 7 is a schematic view generally illustrating the operation of thestraightening and tensioning machine of this invention;

FIG. 8 is a view in perspective of a portion of a straightening andtensioning machine in accordance with this invention;

FIG. 9 is a view in perspective of the machine of FIG. 8, shown with ahammer striking a circular saw blade;

FIG. 10 is a view in perspective of a carriage of the machine of FIG. 8;

FIG. 11 is a top plan view of the machine of FIG. 8;

FIG. 12 is a fragmentary view in left side elevation of a saw bladedrive means of the machine of FIG. 8;

FIG. 13 is a fragmentary view in right side elevation of the saw bladedrive means of FIG. 12;

FIG. 14 is a fragmentary side view, partially in section, of a sawblade-deflecting means of the straightening and tensioning machine ofFIG. 8, with the saw blade lowered onto an anvil;

FIG. 15 is a fragmentary side view, partially in section, of the sawblade-deflecting means of FIG. 14, showing the saw blade held in adeflected configuration;

FIG. 16 is a view in perspective of the saw blade-deflecting means ofFIGS. 14 and 15;

FIG. 17 is a schematic diagram illustrating electrical circuitry for themachine of FIG. 8;

FIG. 18 is a view in perspective of an alternative embodiment of thestraightening and tensioning machine of this invention; and

FIG. 19 is an exploded view in perspective of a sensor mount assembly ofFIG. 18.

THE METHOD

Referring now to the drawings, FIGS. 1-7 illustrate the principles uponwhich the improved method and machine for straightening and tensioningsaws are based. A circular saw blade 11 may be held at one edge by afirst supporting means 12 and by second supporting means 14 at anopposite edge. If a center-biasing means 15 is used to depress thecentral portion of the saw blade, it will be elastically bent about anaxis parallel to a diameter so that its major surfaces lie in curvedplanes. This curvature is shown by the application of a straight edge 16in FIG. 1. Note that in FIG. 1 the straight edge is supported at its endportions and that there is clearance under the central portion of thestraight edge.

At right angles to a line connecting the first supporting means 12,center-biasing means 15, and second supporting means 14, no deflectionwould be evident in a properly tensioned saw blade, as is shown by astraight edge 17 in FIG. 2, which is in contact with the blade over theentire length of the straight edge.

By controlling the amount of relative vertical motion of thecenter-biasing means 15 and the supporting means 12 and 14, thedisplacement of the center of the saw blade 11 with respect to its outeredge can be precisely controlled. It should be noted however that, aswill be discussed in greater detail subsequently, the exact curvatureassumed by the saw blade 11 depends not only on the amount ofdisplacement but upon other parameters of the saw, of particularsignificance being the distribution of tension within the saw.

During the manufacturing and heat treating steps to which a saw blademust be subjected, it is highly likely that an uneven distribution ofresidual tension stress will be produced and that certain areas, such asdefects 19 and 20 illustrated in FIG. 3, will be produced wherein thetension is significantly greater or less than that in the surroundingareas of the saw blade. These defects may be of any shape or size andare not readily detectable in the saw. However, if the saw blade 11 isbowed in the manner shown in FIGS. 1 and 2, these defects becomedetectable. As shown diagrammatically in an exaggerated fashion in FIG.4, when the saw blade 11 is deflected into a curved form, a tightsurface area such as the defect 19 will tend to pull inwardly as a chordspanning a portion of the curvature because its tension is greater thanthat of the surrounding areas of the saw blade. Thus this portion willappear to be raised from the concave surface of the blade above itsproper position, which is shown by a dashed line 19a in FIG. 4. Askilled craftsman can utilize a straight edge to detect this defect andmap it on the surface of the saw so that he may subsequently cure thedefect by hammering. It should be noted that a "loose" portion of thesurface area, having less residual tension stress than the surroundingsurface, would fall away from the natural curvature of the saw blade.However, such loose areas are relatively rare and tend to disappear asthe relative tension of the rim of the saw is increased.

As was indicated in connection with FIGS. 1 and 2, the deflection of thecenter of the saw produced by the center-biasing means 15 with respectto the supporting means 12 and 14 can be precisely controlled. However,the precise curvature that the saw blade 11 will assume depends largelyon the tension distribution in the saw. A dashed line 21 in FIG. 5represents the curvature that would be assumed by a bowed saw having adesired tension distribution. The saw blade 11 illustrated in FIG. 5does not, however, conform to the desired curvature 21; the centralportion of the saw blade falls inside of this curve, while the rim ofthe saw blade extends outside. This represents a saw blade which is"loose on the outside", and may be corrected by hammering the innerportion of the blade to relieve tension in that area.

The saw blade 11 as illustrated in FIG. 6 also fails to conform to thedesired curvature 21. Here, however, the inner portion of the sawremains outside the curve, while the rim falls inside. This is aconfiguration known as "loose in the center" and can be corrected byproper hammering near the rim of the saw.

These and other distortions and tensioning defects can be corrected bythe use of a method and machine for tensioning and straightening saws inaccordance with this invention. The theory of operation of this methodand machine can be explained by reference to FIG. 7, which illustratesthe circular saw blade 11 in the bowed configuration described inconjunction with FIGS. 1 and 2, held by supporting means 12 and 14 anddished by the center-biasing means 15. A sensor 22 is positioned at apredetermined distance over the saw blade 11. The sensor 22 may be ofany type having sufficient sensitivity to detect the minute deviationsin the distance to a small local area of the blade surface which areindicative of both surface distortions and tensioning defects. Eitherelectrical, mechanical or pneumatic sensing may be utilized; in thepreferred embodiment, the sensor 22 is a proximity detector of a typewell-known in the art, capable of determining by electromagneticinduction whether a metallic object is at a preset distance from thesensor.

Bowing of the saw blade 11 into a predetermined curvature enables localdefects as shown in FIGS. 3 and 4, and overall maldistribution oftension as shown in FIGS. 5 and 6, to be detected by the sensor 22. Thesensor is maintained a predetermined distance from the saw, and itssensitivity is adjusted to detect any points on the surface of the sawthat are closer to the sensor than would be found in aperfectly-tensioned and perfectly-straightened saw. The sensor and sawblade must then be moved relative to each other so that the sensorsweeps substantially the entire surface of the saw blade for suchdetection. It is sufficient to limit the detection to those points whichprotrude from the concave surface, and which represent either surfacedeformities or tight spots of excess tension. Loose spots of low tensionare corrected by hammering the tight spots, since this redistributes thetension more uniformly.

This relative motion may be accomplished in many ways. The sensor mayremain fixed while the saw blade is moved relative to the sensor, thesensor may be moved over the surface of the saw blade while the sawblade remains stationary, or a combination of motions of both the sensor22 and the saw blade 11 may be used. In the preferred embodiment, thesensor traces a helical path in its examination of the surface of thesaw blade. This form of path is particularly useful in view of thecircular shape of the saw blade, as it provides the most efficientcoverage of the surface of the saw with the simplest mechanical motions.

With the preferred manner of dishing the saw, it will be readilyapparent that it would be complicated to have the sensor 22 move in ahelical path over the surface of a stationary saw. The sensor 22 wouldhave to be made to follow a complicated vertically reciprocating path aswell as a helical horizontal path as it traveled around the surface ofthe blade. It should be noted, however, that were the saw blade 11 to bedished into the general form of a segment of an oblate spheroid, itmight be a reasonable procedure to physically move the sensor in ahelical path above the surface of a stationary saw.

The preferred method of examining the surface of the saw blade 11 is torotate the blade about its center while maintaining the supporting means12 and 14 in fixed positions, so that during each revolution eachportion of the blade will be flexed successively into the configurationillustrated in FIG. 7, when in alignment with the supporting means 12and 14 and the center-biasing means 15. If the blade is rotated whilethe blade and the sensor 22 are moved linearly with respect to eachother so that the sensor effectively reciprocates or oscillates betweenthe position of the second supporting means 14 and that of thecenter-biasing means 15, helical paths covering substantially the entiresurface of the saw blade 11 will be traced by the sensor. This relativereciprocating action can be provided by physically moving either thesensor 22 or the saw blade 11.

An added requirement is that the distance from the sensor 22 to thewarped plane of curvature of the surface of a properly-tensioned andstraightened saw blade be kept constant, so that deviations from thisplane due to tension and surface defects may be detected. Accordingly,the path of relative motion of the sensor 22 over the saw blade 11 mustlie in a curved plane parallel to that of the ideal blade shown by thedashed line 21 of FIGS. 5 and 6, displaced, however, from the latter bythe desired amount.

Preferably positioned in vertical alignment with the sensor 22 are ahammer 24 and an anvil 25. To maintain this alignment, the hammer andanvil must be moved with the sensor, in the case where the sensor 22 isphysically moved with respect to the saw blade 11. The anvil 25 shouldnot, however, be moved vertically; its upper surface 25a should be heldin a predetermined vertical location, which will be further definedsubsequently.

During the sensing of the saw blade 11 by the sensor 22, the relativehelical motion of the sensor and blade continues without interruption,so long as the portions of the surface being sensed are not closer tothe sensor 22 than the predetermined distance. However, whenever thesensor 22 detects a "high spot", i.e., a point on the blade closer tothe sensor than the predetermined distance, relative motion of thesensor and saw blade stops. The sensor has now detected a point thatmust be hammered.

The high spot on the surface of the saw may represent a bend or kink, ora tight spot or surface discontinuity under excess tension, or thetighter portion of an improperly tensioned saw blade, such as thecentral portion shown in FIG. 5 or the outer portion shown in FIG. 6.Any of these defects can be corrected by hammering.

To accomplish the hammering, the saw blade 11 is lowered to the positionshown as a dashed line in FIG. 7 at 11A. This may be accomplished bylowering the supporting means 12 and 14 to the positions shown as 12Aand 14A, respectively. It should be noted, however, that since therelease of the saw blade from its bowed form is done only to place theblade on the anvil 25, it is only necessary to lower the secondsupporting means 14. This action will place the portion of the saw bladeto be hammered on the upper surface 25a of the anvil, which ismaintained in a suitable position for that purpose.

Before the saw blade can be struck by the hammer 24, the sensor 22 mustbe removed from its sensing position. This can be done in substantiallyany direction and by any convenient means, so long as the sensor isoutside the path of the hammer 24 when it is released. The hammer 24 isthen released and falls, striking the saw blade sharply at the pointwhere the high spot was detected. This point will be straightened if itis a physical bend in the saw, and will be loosened if it is a spot ofexcess tension.

The hammer 24 is then lifted from the saw blade 11. When the sensor 22has been moved back to its operating position and the saw blade 11 againbowed by the supporting means and biasing means, sensing operationbegins again. If the spot which has just been hammered still shows as ahigh spot, no relative motion of the sensor and blade will occur, andthe hammering cycle will repeat itself until the spot conforms to thedesired curvature. Once this has been accomplished, the relativesweeping motion of the sensor and saw blade resumes, being stopped againfor the hammering of any further high spots that may be detected. Afterall discovered defects have been removed from one surface of the sawblade, it is turned over to treat the other surface. This treatment maybe repeated as many times as desired, and with whatever sensitivity isdeemed necessary, to accomplish the level of precision of tensioning andstraightening needed for any particular saw blade.

The sensing and hammering operations preferably proceed from the outeredge of the saw blade toward the center. If a tight region or a bulgeextends inwardly for some radial distance, hammering the outer portiontends to relieve the inner portion as well.

THE MACHINE - FIRST EMBODIMENT

A preferred form of tensioning and straightening machine 30 inaccordance with this invention is illustrated in FIGS. 8-17. In thisembodiment, the hammer 24 and anvil 25 (see FIG. 9) remain fixed inposition, as does the sensor 22 during sensing operations, while thecircular saw blade 11 is moved with respect to these elements. Toprovide the relative movement required for sensing, the saw blade 11 ismounted on a carriage 31 which is driven in a reciprocating oroscillating motion by a motor 32 (FIG. 9). A saw blade drive assembly 34is mounted on the carriage 31 and is driven by a motor 35 to providecircular motion for the saw blade 11.

The carriage 31, as is best shown in FIG. 10, is preferably constructedof metal and may be of any convenient shape and size adequate formounting the necessary components for stressing and rotating the sawblade. The carriage 31 is connected to a pair of parallel carriage arms36 by a pair of hinge bolts 37. The carriage arms 36 are connected attheir other ends by an additional pair of hinge bolts 39 to a pair ofsubstantially identical carriage mount assemblies 40. To provide freelateral reciprocating motion of the carriage 31 with respect to thecarriage mount assemblies 40, care should be taken to see that the hingebolts 37 and 39 are all parallel to each other.

Each carriage mount assembly 40 preferably comprises a lower mountingplate 41, an upper mounting plate 42, a pivot rod 44 and a mountingframe 45. The mounting frame 45 is attached to the carriage arm 36 bythe hinge bolt 39 and is secured to the upper mounting plate 42 in amanner to prevent any relative motion between the mounting frame 45 andupper mounting plate 42. The lower mounting plate 41 may be bolted orotherwise attached to any suitable base. In the preferred embodiment,corresponding grooves 46 are provided in an upper surface of the lowermounting plate and a lower surface of the upper mounting plate toaccommodate the pivot rod 44. The combined depths of the grooves shouldbe, however, less than the diameter of the pivot rod 44 so that, absentother securement, the upper mounting plate would rock back and forth onthe lower mounting plate with the pivot rod 44 being the pivot.

This construction permits the upper mounting plate 42 to move through anangle, shown as 47, with respect to the lower mounting plate. Becausethe mounting frame 45 is integrally secured to the upper mounting plate42, it, in turn, can move through an equivalent angle shown as 49. Bythis arrangement, the mounting frame can be placed at any desiredinclination with respect to the vertical, within the range of the angle49, for reasons which will be subsequently explained. With the mountingframe in the desired position, a pair of bolts 50, positioned atopposite sides of the pivot rod 44, are tightened through openings inthe upper mounting plate 42 into threaded openings in the lower mountingplate 41, thus pulling against each other to fix the position of theupper mounting plate 42 and, accordingly, the mounting frame 45.

To maintain the desired parallel alignment of the hinge bolts 37 and 39,each of the mounting frames 45 must be positioned at the same angle withrespect to the vertical. It should be readily apparent from anexamination of FIG. 10 that the carriage 31, swinging on the carriagearms 36, will sweep a generally circular path with respect to themounting frames 45. If the carriage mount assemblies 40 are adjusted sothat the mounting frames 45 and thus the hinge bolts 37 and 39 areexactly vertical, the entire circular motion of the carriage 31 will bein a horizontal plane having no vertical displacement, as it moves fromone end of its sweep to the other. If the mounting frames 45 are shiftedthrough an angle from the vertical in the manner previously described sothat the hinge bolts 37 and 39 are also shifted from the vertical, thecarriage will maintain the same circular motion with respect to themounting frames 45. However, the circle through which the carriage moveswill no longer be in a horizontal plane. There will be a definite andcontrollable vertical displacement, generally tracing a portion of anellipse when projected on the horizontal plane. If the frames 45 aretipped backwardly in a counterclockwise direction as shown in FIG. 10,the low points of carriage movement are reached when the arms 36 areswung to their extreme positions, and the carriage attains its highestpoint when the arms are midway between their extremes as shown. Thecarriage sweeps an oscillatory path as suggested by the arrow 51. Thebowed saw blade is lower in the center than at the edges, as shown inFIG. 7. By properly adjusting the angle at which the frames 45 areinclined to the vertical, the carriage 31 can be made to follow a pathwhich is an inverted image of the curvature of the bowed saw blade. Witha properly tensioned saw blade having no substantial surface defects,the swinging motion of the carriage and a blade mounted thereon cancelsout the curvature of the blade and maintains a constant distance betweenthe stationary sensor and the surface of the moving blade. The sensorthereby responds only to defects in the blade, and is unaffected by thecurvature caused by intentional bending.

The carriage motor 32 which provides the reciprocating motion of thecarriage 31 is mounted on a gimbal 52 pivoted in a mounting bracket 54,which is independently attached to the base by a bolt 55 or otherfastener. A carriage drive shaft 56 is threaded into a gimbal nut 57(FIG. 8), which is pivoted in a mounting bracket 59 on the carriage 31.The extent of the sweep of the carriage 31 in either direction iscontrolled by a limit switch 60 (FIG. 9) and a limit switch 61 (FIG.11), which are independently mounted on the base and positioned to beoperated by the approach of opposite ends of the carriage 31. The modeof operation of the limit switches 60 and 61 will be described in detailin the discussion of FIG. 17. When the carriage 31 interacts with eitherlimit switch 60 or 61, the carriage motor 32 is reversed, causing achange in the direction of rotation of the carriage drive shaft 56.Because this drive shaft is threaded through the gimbal 57 on thecarriage 31, this change in its rotation causes a reversal in thedirection of motion of the carriage 31. In this manner an oscillatingmotion of the carriage 31 is provided, the gimbals 52 and 57 preventingjamming or misalignment of the carriage drive shaft 56 which mightotherwise be produced by the arcuate motion of the carriage.

The saw blade drive assembly 34 is best illustrated in FIGS. 12 and 13and has a base 65 which is machined to rest on opposite parallel sidesof the carriage 31. The base may accordingly be positioned in anydesired location on the carriage 31 to accommodate saws of variousdiameters, in a manner to be later described herein. The base 65 isclamped in position on the carriage 31 by placing a clamping bar (notshown) beneath the carriage and fitting a pair of elongated clampingbolts 66 through aligned openings in the clamping bar and base. Bytightening a pair of nuts 67, the base 65 and clamping bar are pulledtoward each other, locking the saw blade drive assembly 34 in positionon the carriage 31 in a well-known manner.

An upper drive arm 69 has a pair of ears 69a (see FIG. 11) at one endand is secured to an upper attachment lug 70 by a shaft 71 passedthrough corresponding openings in the ears 69a and the upper attachmentlug. This means of attachment permits pivotal motion between the upperdrive arm 69 and the base 65. A lower drive arm 72 shown in FIGS. 12 and13 is similarly constructed and is attached to a lower attachment lug 74on the base 65 by a shaft 75 to permit pivotal motion between the lowerdrive arm and the base.

Mounted on the shaft 71 on one side of the saw blade drive assembly 34,as shown in FIG. 12, is a drive gear 76. Driven gears 77, 79 and 80 aremounted, respectively, on the shaft 75 and shafts 81 and 82.

On the side of the saw blade drive assembly 34 opposite the gears 76-80(see FIG. 13) are a lower drive wheel 84 and an upper drive wheel 85which are mounted, respectively, on the shaft 81 and the shaft 82 andare positioned to engage the rim of the circular saw blade 11therebetween to produce rotation of the blade. The lower drive wheel 84is preferably a solid metallic part while the upper drive wheel 85preferably has an outer rim 86 of rubber or other suitable cushioningmaterial.

Both the upper drive arm 69 and lower drive arm 72 must be accuratelyfixed in position to firmly engage the saw blade 11 between the drivewheels 84 and 85, and to locate the blade precisely. To this end,adjustable attachment means are used to position and hold the drive arms69 and 72 in place. These are preferably attached to cylindrical rods 87which are rotatably received in holes 89 in the arms and the base 65. Bysecuring the attachment means to these rods, proper alignment ofthreaded openings with threaded members can be maintained regardless ofthe relative angles the drive arms 69 and 72 make with the base 65.

A spacer bolt 90 (FIG. 12) is threaded through a pin 87 in the base 65and abuts the lower drive arm 72 to adjustably define the upper limit oftravel of this arm. A draw bolt 91 (FIG. 13) passes freely through anunthreaded opening in the base 65 and is threaded into a pin 87 in thelower drive arm 72. Upon being tightened, the bolt 91 draws the lowerdrive arm firmly against the spacer bolt 90, fixing the arm in adjustedposition.

The lower limit of travel of the upper drive arm 69 is adjustably fixedby a spacer bolt 92 (FIG. 12), which is threaded through a pin 87 inthis arm and abuts the base 65. A nut 94 is threaded on a stud 93 whichpasses freely through the arm 69 and is fixed in a pin 87 in the base65. Tightening the nut 94 draws the upper drive arm 69 against thespacer bolt 92. If desired, compression springs 95 and 96 may be placedaround the draw bolt 91 and the stud 93, respectively, to spread thedrive arms from the base when the draw bolt 91 and the nut 94 areloosened. It should be noted that it may be convenient to replace thenut 94 and stud 93 with a more rapid clamping device, such as anair-operated actuator, to provide for more rapid attachment and releaseof circular saw blades 11 in the drive assembly 34.

A metal block 97 is secured to the upper drive arm 69 by a plurality ofthreaded fasteners 99 (see FIG. 11) to hold an elongated positioning bar100 of the center biasing means 15 in place. The center biasing means 15is best illustrated in FIGS. 9 and 11, and has a center stud 101 whichis attached at one end of the positioning bar 100 and is of anappropriate size to fit into a center hole of the circular saw blade 11.A peripheral lip 102 may be provided on the center stud 101 to performthe center biasing function previously described with reference to FIG.7. However, with some saws it may be desirable to utilize the centerstud 101 solely for fixing the position of the center of the saw blade11, and to utilize a separate biasing means such as the screw 104illustrated in FIG. 8 to perform the bowing function. Such separatebiasing means might be useful with saws having diamond or other shapeknockouts at the center, such saws being familiar to those skilled inthe art. As the center biasing means 15 is affixed to the upper drivearm 69, the nut 94 controls not only the clamping of the saw bladebetween the drive wheels 84 and 85, but also the positioning and centerbiasing of the saw blade 11 by the center biasing means.

Operating power for the drive wheels 84 and 85 is conveyed by a driveshaft 105 (see FIG. 8, 9 and 12) which is keyed into the shaft 71 of thedrive gear 76. The drive shaft 105 may be connected through a pair ofuniversal joints 106 to prevent alignment problems with respect to thesaw blade drive motor 35. The motor 35 may be secured to the carriage 31as shown in FIG. 8, or may alternatively be mounted directly on the sawblade drive assembly 34.

Because the center biasing means 15 fixes the position of the center ofthe saw blade, the saw blade 11 may be rotated in the desired manner bymoving the rim in either direction between the drive wheels 84 and 85.The adjustability provided for the upper drive arm 69 and the lowerdrive arm 72 by the spacer bolts 90 and 92, the draw bolt 91, and thenut 94 permits proper alignment of the drive wheels 84 and 85 with thesurfaces of the saw blade. To prevent any distortion of the saw blade asit is being rotated, it is desirable that the centers of the drivewheels be vertically aligned with each other. If the centers are not invertical alignment, the rim of the saw blade might be twisted, causingerrors in the hammering operation. After the desired position for thelower drive arm 72 has been determined, it is preferably tightened andkept in place; when saw blades of different thicknesses are to behammered, the upper drive arm 69 is loosened, adjusted to the properheight, and re-tightened.

After tightening the nut 94 with a saw blade 11 in place as shown inFIG. 13, the drive motor 35 is actuated to rotate the saw blade aboutthe center stud 101 of the center biasing means 15. Motion is translatedfrom the motor 35 to the saw blade 11 by the drive shaft 105, whichturns the drive gear 76 in a direction shown, for example, by an arrow107 in FIG. 12. The drive gear 76 causes the driven gears 77, 79 and 80to rotate in directions shown by arrows 109. Motion of the driven gear79 is passed by the shaft 81 to the lower drive wheel 84, which rotatesin a direction shown by an arrow 110 in FIG. 13. Motion of the drivengear 80 is translated through the shaft 82 to the upper drive wheel 85,which rotates in a direction shown by an arrow 111 in FIG. 13. The drivewheels 84 and 85 rotate in opposite angular directions so that adjacentportions of the drive wheels move in the same linear direction, rotatingthe saw blade 11 in the desired manner.

It should be noted that the lower drive wheel 84 performs the functiondescribed for the first supporting means 12 of FIG. 1, in addition toaiding in the rotation of the saw blade 11. The function of the secondsupporting means 14 is performed by a saw blade lift assembly 115 bestillustrated in FIGS. 14-16.

The saw blade lift assembly 115 has a base 116 which is preferablymounted on the carriage 31 in a manner substantially identical to themounting of the base 65 of the saw blade drive assembly 34. The base 116is placed on the carriage 31 in the manner illustrated in FIG. 8 andclamping bolts 117 are passed through openings in a clamping bar (notshown) beneath the carriage 31 and through openings 119 (FIG. 16) in thebase 116. Nuts 120 (FIGS. 8 and 9) tighten the base 116 against theclamping bar to hold the saw blade lift assembly 115 firmly in position.

One or more substantially vertical mounting beams 121 are securelyattached to the base 116 by threaded fasteners 122 passed through amounting ear 121a on each beam 121. An upper cross beam 124 and a lowercross beam 125 are pivotally mounted by connectors 126 to the mountingbeam 121. A vertical operating beam 127 is pivotally attached byconnectors 129 to the upper cross beam 124 and lower cross beam 125.

Attached to the base 116 is a pair of air cylinder mounting legs 130 towhich an air cylinder 131 is pivotally attached by a connector 132. Anoperating rod 134 of the air cylinder 131 is pivotally attached to thelower cross beam 125.

The mounting beam 121, upper cross beam 124, lower cross beam 125 andoperating beam 127 form a pivotally-connected parallelogram linkage, sothat when compressed air is supplied to the air cylinder 131 to forcethe operating rod 134 upwardly, the beams 124, 125 and 127 pivotupwardly with respect to the mounting beam 121 attached to the base 116.The beam 127 remains in its vertical orientation and undergoes verylittle horizontal displacement through the short arc of its travel.

Attached to the operating beam 127 is a bifurcated lift member 135. Apair of lift screws 136 may be mounted directly in the lift member 135or, as shown, in a pair of extension legs 137 attached to the liftmember by fasteners 139.

The use of extension legs 137 to hold the lift screws 136 affords greatversatility to the saw blade lift assembly 115. As was explained withrespect to FIGS. 1 and 2, the saw blade lift assembly 115, acting inconjunction with the center stud 101 of the center biasing means 15 andof the lower drive wheel 84 of the saw blade drive assembly 34, providesthe desired bowed curvature to permit sensing of the saw blade 11. Aswill be explained further, the saw blade is sensed over a portion of itssurface extending substantially from the center stud 101 to the sawblade lift assembly 115, so that the relative elevations and positionsof the lift screws 136 are very important to proper tensioning andstraightening.

One advantage ensues simply from the use of two lift screws. Thispermits the sensor 22 to examine points located between the lift screwsrather than over them, so that it is highly unlikely that a defectriding over one lift screw will produce errors in the readings of thesensor, although such a problem could easily occur if a single liftscrew were utilized. For example, if a ridge or bump protruding from theupper surface of the saw blade were to pass over a single lift screwpositioned directly beneath the sensor, the correspondingly-concavelower surface of the saw blade resting on the lift screw would permitthe upper surface, although deformed, to remain at the proper distancefrom the sensor. By the use of two separated lift screws 136, the lowersurface is supported at points removed from the sensed region, so thatwhen a defect passes under the sensor it will be correctly detected.

The use of extension legs 137 also permits the lift screws 136 to bepositioned either close together or far apart, as may be required tobest accommodate a wide variety of saw diameters. This gives thetensioning and straightening machine 30 greater versatility.

The relative heights of the lift screws 136 can be adjusted to permitfine adjustment of the curvature of the saw blade 11, thereby adding tothe ability of the machine to accurately match the curvature of aproperly straightened and tensioned saw to the reversed image of thesweep of the carriage.

When a saw blade 11 is placed on the carriage 31, the saw blade liftassembly 115 is positioned as shown in FIG. 14, with the lift screws 136lowered beneath the level of the upper surface 25a of the anvil 25. Inthis position, the saw blade 11 is undistorted, and rests firmly andsquarely on the anvil 25. When it is desired to sense the saw blade 11,the air cylinder 131 is activated so that the operating rod 134 pushesupwardly and the lift screws 136 lift the edge of the saw blade 11 fromthe anvil 25. The blade, being held by the center stud 101 and the wheel84, is bent by the lift screws into a predetermined bowed curvature.When a defect is found on the surface of the saw blade 11 so thathammering is required, the air pressure is released from the aircylinder 131 so that the saw blade lift assembly 115 returns to theposition shown in FIG. 14 and the saw blade 11 is released to drop ontothe anvil 25.

The hammer 24 and its associated operating hardware are best illustratedin FIGS. 8, 9 and 11. A mounting plate 140 is rigidly affixed to asupporting pillar 141, which is in turn firmly mounted independently ofthe carriage 31. A pair of bearings 142 are attached to the mountingplate 140 and pivotally hold a pivot arm 144 of a striker block 145therein. The hammer 24 is mounted on a shaft 146. The shaft 146 isattached to a pivot arm 147 (FIG. 11) which is journaled in bearings(not shown) within the pivot arm 144 of the striker block 145. By thisconstruction, the hammer 24 is enabled to pivot independently of thestriker block 145 while moving arcuately about the same axis.

An elastomeric bushing 146a is mounted on the shaft 146 and positionedin an opening 149 in the striker block 145. The opening 149 is somewhatangularly elongated, and has an upper surface 149a and a lower surface149b having contours substantially matching those of the bushing 146a.The bushing 146a provides cushioning during impact of the striker block145 against the shaft 146, but is sufficiently firm to avoid materiallylessening the impact of the hammer 24 against the saw blade 11. A magnet150 is attached to the mounting plate 140 for normally holding the shaft146 of the hammer 24 in its fully raised position as shown in FIG. 8.

An air cylinder 151 is independently attached to the base of themachine, and has an operating rod 152 which is connected by a suitablepin 154 or other pivotal attachment means to an ear 155 on the strikerblock 145. The air cylinder 151 is preferably of the double-acting type,having air hoses connecting either side of an internal operating pistonto a suitable valve (not shown) of a type which is operable to drive theoperating rod 152 selectively in an upward and downward direction. Suchan arrangement is well known to those skilled in the art, and will notbe described further.

While the sensor 22 is scanning the saw blade 11, the hammer 24 is heldin the raised position shown in FIG. 8 by two independent means. Themagnet 150 holds the shaft 146 with sufficient force to prevent thehammer 24 from falling. Additionally, the air cylinder 151 maintains theoperating rod 152 in its uppermost position so that the shaft 146 issupported by the lower surface 149b of the opening 149 in the strikerblock 145. When a defect in the blade has been sensed, the sensor 22 isremoved from its position above the saw blade 11 and the saw blade islowered onto the anvil. Then a valve is actuated which causes the aircylinder 151 to pull down sharply on the operating rod 152, acceleratingthe striker block 145 downwardly. However, it should be noted that thehammer 24 remains in place, supported by the magnet 150, until thestriker block 145 has moved a sufficient distance so that the uppersurface 149a of the opening 149 strikes the bushing 146a on the shaft146. When this occurs, the hammer 24 is snapped downwardly, firmlystriking the saw blade 11 as it reaches the lowered position illustratedin FIG. 9.

After the hammer 24 has struck the saw blade, the control valve isactuated to cause the air cylinder 151 to force the operating rod 152upwardly, raising the striker block 145. The lower surface 149b of theopening 149 pushes upwardly on the bushing 146a so that the hammer 24 israised back into the position shown in FIG. 8. Upward motion of thestriker block 145 is stopped when the shaft 146 comes into contact withthe magnet 150.

The sensor 22 and means for mounting it and controlling its operationare best illustrated in FIGS. 8, 9 and 11. The sensor is mounted on asensor arm 160, which is pivotally supported on a hinge bracket 161(FIG. 8) attached to an independent supporting pillar 162, for arcuatemovement in a generally horizontal plane. Attached to the top of thepillar 162 by a bolt 164 are a sensor drive motor mounting plate 165 anda sensor drive switch mounting arm 166. A sensor drive switch 167 isattached to the mounting arm 166.

A sensor drive motor 169 is attached beneath the mounting plate 165. Acrank 170, which may be in the form of a disk (as shown) or a rod, isdrivingly connected with the sensor drive motor 169 to convert itsrotary output into reciprocating motion in a well-known manner. A sensordrive rod 171 (FIG. 8) is pivotally connected at 173 and 176 with thecrank 170 and the sensor arm 160, respectively, so that thereciprocating motion produced by the crank 170 is imparted to the arm160 and sensor 22.

When the sensor 22 reaches its operating position over the saw blade 11,as shown in FIG. 8, the sensor arm 160 abuts the sensor drive switch 167which, as will be hereinafter described, stops the annular motion of thesensor arm toward the center of the saw blade. Accordingly, it can beseen that the location of the sensor drive switch 167 determines theoperating position of the sensor 22.

When the sensor 22 detects a defect which must be hammered, the sensordrive motor 169 is actuated to turn the crank 170 in an angulardirection which causes the sensor drive rod 171 to retract the sensorarm 160 and sensor away from their operating positions over the sawblade. An air switch 172 is mounted to be actuated by motion of thesensor arm 160 shortly after it begins its retracting movement away fromthe saw blade 11. The air switch 172 is connected through suitable hosesand valves (not shown) to the air cylinder 131 of the saw blade liftassembly 115 in such fashion that the retraction of the sensor arm 160releases pressure from the air cylinder, so that the saw blade liftassembly 115 lowers the saw blade onto the anvil 25 and into theundeflected position illustrated in FIG. 14.

As the sensor arm 160 reaches the outward limit of its travel as shownin FIG. 9, a camming plate 174 attached to the arm actuates an airswitch 175, which is connected by suitable hoses and valves (not shown)to the air cylinder 151 that operates the hammer 24. Actuation of theair switch 175 causes the hammer 24 to strike the saw blade 11 in themanner previously described. It should be noted that the hammer thuscannot be caused to strike the saw blade until the arm 160 and sensor 22have been completely removed from its path.

Upon reaching the end of the retracting motion, the direction of travelof the sensor arm 160 is reversed by continued rotation of the crank170, withdrawing the camming plate 174 from the air switch 175. Thisactuates the air cylinder 151 to raise the hammer back to the positionshown in FIG. 8, where it is supported both by the pressurization of theair cylinder 151 and the attraction of the magnet 150.

The continuation of the motion of the sensor arm 160 toward the centerof the saw blade 11 causes the arm to engage the air switch 172,pressurizing the air cylinder 131 to lift the saw blade 11 into a bowedconfiguration raised from the anvil 25, as shown in FIG. 15. It isdesirable that the saw blade be deflected into this configuration priorto the sensor 22 reaching its operating position, so that vibrationswhich may be produced in the saw blade when it is lifted can damp outnaturally before the sensing operation beings. Owing to the highsensitivity of the sensor 22, a vibration in the saw blade mightotherwise be detected as a defect and inadvertently hammered.

Continuing motion of the sensor arm 160 brings the sensor 22 to itsoperating position over the saw blade. At this point, the sensor arm 160engages the switch 167, deenergizing the sensor drive motor 169 to stopthe motion of the sensor. The sensing operation, which will later bedescribed, then begins.

THE CONTROL CIRCUIT

The electrical circuitry for controlling the operation of the tensioningand straightening machine is illustrated in FIG. 17. A direct currentpower supply 180 provides operating power for the motors and relays. Itshould be noted, however, that other embodiments may utilize alternatingcurrent for powering relays or motors. A conductor 181 connects oneterminal of the power supply 180 to the sensor drive switch 167. Aconductor 182 connects the other terminal of the power supply 180 to ajunction 184.

A conductor 185 is connected from the conductor 181 through a normallyopen contact 186a of a relay 186, a junction 187, the armature of thesaw blade drive motor 35, a junction 189, an a normally open contact186b of the relay 186, to the conductor 182. Each of the motors ispreferably shunt wound and has a separately excited field. A conductor190 serially connects a normally closed contact 186c of the relay 186, aresistor 191 and a normally closed contact 186d of the relay 186 betweena junction 187 and a junction 189 with a conductor 185.

A conductor 192 is connected from the conductor 181 through a normallyopen contact 186e of the relay 186, a junction 194, a normally closedcontact 195a of a relay 195, a junction 196, a normally open contact195b of the relay 195, a junction 197, and a normally open contact 186fof the relay 186, to the conductor 182. Serially connected between thejunction 194 and the junction 197 by a conductor 199 are a normallyclosed contact 186g of the relay 186, a resistor 200, and a normallyclosed contact 186h of the relay 186. Serially connected between thejunctions 194 and 197 by a conductor 201 are a normally open contact195c of the relay 195, a junction 202, and a normally closed contact195d of the relay 195. The armature of the carriage motor 32 isconnected between the junction 196 and the junction 202.

A conductor 204 is connected between the conductors 181 and 182 andserially connects a normally open contact 205a of a time delay relay205, a junction 206, the armature of the sensor drive motor 169, ajunction 207 and a normally open contact 205b of the time delay relay205. A normally closed contact 205c of the time delay relay 205 and aresistor 209 are serially connected by a conductor 210 between thejunctions 206 and 207.

A conductor 211 serially connects the normally closed limit switch 60,the normally open limit switch 61, and the winding 195w of the relay195, between the conductors 181 and 182. A normally open contact 195e ofthe relay 195 is connected across the limit switch 61.

The sensor drive switch 167 is a single-pole double-throw switch havingterminals 167a and 167b. The terminal 167a is connected by a conductor212 through a junction 213, a normally closed contact 214a of a sensorrelay 214, and a winding 186w of the relay 186, to the junction 184. Aconductor 215 connects the terminal 167b of the sensor drive switchthrough a junction 216 and a winding 205w of the time delay relay 205 tothe junction 184. A normally open contact 214b of the sensor relay 214is connected between the junction 213 and the junction 216.

The sensor 22 is independently controlled and is powered by a lowvoltage power supply 217. The sensor is connected by conductors 219 to asignal control module 220, which is connected by conductors 221 to thepower supply 217 and by conductors 222 to a winding 214w of the sensorrelay 214. The signal control module 220 controls energization of thesensor 22 from the power supply 217, while the output of the sensorcontrols energization of the winding 214w of the sensor relay 214 by thesignal control module.

Operation of the circuitry of FIG. 17 will now be described. The powersupplies 180 and 217 are turned on, energizing the circuits. If thesensor 22 and its arm 160 are in the operating position illustrated inFIG. 8, and the sensor is over a portion of a saw blade whose surfacecoincides with the predetermined desired curvature, the sensor 22 willproduce no output, and the winding 214w of the sensor relay 214 will notbe energized.

The determination of which of the motors 32, 35 and 169 are energizedultimately depends on whether the winding 186w of the relay 186 or thewinding 205w of the time delay relay 205 is energized. It can be seenthat this is determined by the condition of the sensor drive switch 167.With the sensor arm 160 in the operating position shown in FIG. 8, thesensor drive switch 167 is biased by the arm so that contact is madewith the terminal 167a. Thus, the relay 186 is energized by a circuitfrom the power supply 180 through the conductor 181, the sensor driveswitch 167, the closed sensor relay contact 214a, the conductor 212, thewinding 186w, and the conductor 182.

When the winding 186w is energized, normally open contacts 186a, b, eand f are closed and normally closed contacts 186c, d, g and h areopened. This completes a circuit energizing both the carriage motor 32and the saw blade drive motor 35. Resistors 191 and 200 are disconnectedfrom across the motors 35 and 32, respectively. The sensor drive motor169 is not energized because the contacts 205a and 205b remain open.Thus, when the sensor arm is in the operating position shown in FIG. 8and no defect has been detected by the sensor 22, the saw blade drivemotor 35 operates to rotate the saw on the carriage, and the carriagemotor 32 operates in one direction of rotation to sweep the carriage,and thus the saw blade 11, past the sensor 22. The sensor drive motor169 does not operate, so the sensor arm 160 and the sensor 22 remainfixed in the operating position.

As has previously been described, the direction of motion of thereciprocating carriage 31 is controlled by the direction of rotation ofthe carriage drive shaft 56 and the carriage motor 32. The relay 195functions as a reversing switch for controlling the direction ofarmature rotation of the carriage motor 32. Operation of the reversingrelay 195 is controlled by the limit switches 60 and 61.

During an initial phase of operation, the winding 186w of the relay 186is energized to operate the motors 32 and 35, but the winding 195w ofthe reversing relay 195 is not energized, being open circuited by thenormally open contact 195e and the normally open limit switch 61.Accordingly, the contacts 195a and 195d are closed, the contacts 195band 195c are open, and current flows from the power supply 180 throughthe conductor 181, the conductor 192, the contact 186e, the contact195a, the carriage motor 32, the conductor 201, the contact 195d, thecontact 186f, and the conductor 182 back to the power supply. It can beseen that current flow through the carriage motor 32 is in the directionshown by an arrow 224 in FIG. 17. Current flow in this directionproduces armature rotation of the carriage motor 32 which moves thecarriage in a direction toward the limit switch 61.

When the carriage reaches the limit switch 61, it closes its contacts tocomplete a circuit from the power supply 180 through the conductor 181,the conductor 211, the limit switches 60 and 61, the winding 195w of thereversing relay 195 and the conductor 182, so that the winding 195w isenergized and operates the contacts of the relay. Contacts 195a and 195dare opened, and contacts 195b, 195c and 195e are closed. Current nowflows through the conductor 181, the contact 186e, the conductor 201,the contact 195c, the carriage motor 32, the conductor 192, the contact195b, the contact 186f, and the conductor 182 to the power supply 180.Current flow is now in a direction opposite that shown by the arrow 224,and the direction of rotation of the armature in the carriage motor 32and, accordingly, the direction of motion of the carriage 31, isreversed. when the carriage moves away from the limit switch 61, theswitch is again opened. However, the contact 195e connected in parallelwith the limit switch 61 provides a holding circuit keeping the winding195w energized after the limit switch 61 has been opened.

At the other end of its travel, the carriage strikes the normally closedlimit switch 60, causing its contacts to open. This breaks the circuitenergizing the winding 195w, and the relay returns to its normalconfiguration with the contacts 195a and 195d closed and the contacts195b, 195c and 195e opened. Current flow through the carriage motor 32again resumes in the direction shown by the arrow 224, and the directionof motion of the carriage reverses. When the carriage leaves the limitswitch 60, its contacts again close. However, because the contact 195eand the limit switch 61 are both open, the winding 195w remainsdeenergized.

The saw blade 11 is thus reciprocated or oscillated with the carriage 31beneath the sensor 22 by the motor 32, while it is rotated by the motor35. Should a defect or improperly tensioned portion of the saw bladecome beneath the sensor 22, this defect is detected and the sensorcauses the signal control module 220 to energize the winding 214w of thesensor relay 214. When this occurs, the contact 214a is opened and thecontact 214b is closed.

The opening of the contact 214a breaks the circuit energizing thewinding 186w, so that the contacts of the relay 186 return to theirnormal conditions. Contacts 186a, b, e and f open so that operatingvoltage is removed from the motors 32 and 35. Contacts 186c and d close,connecting the resistor 191 across the armature of the saw blade drivemotor 35. As will be readily understood by those skilled in the art, theplacement of this load across the motor armature serves as a brake,swiftly stopping the motor 35. Contacts 186g and h place the resistor200 across the armature of the carriage motor 32, so that this motor isalso quickly stopped. The motion of the saw blade is thus arrestedpromptly. It should be readily apparent that the resistor 200 will serveits braking function regardless of the condition of the relay 195, sothat the resistor may be used to stop the motor 32 in either directionof operation.

The closing of the contact 214b of the sensor relay 214 energizes thewinding 205w of the time delay relay 205 through the conductor 181, thesensor drive switch 167 via the terminal 167a, the contact 214b, theconductor 215, and the conductor 182. This closes the contacts 205a and205b and opens the contact 205c. A time delay is provided in the relay205 only upon returning the contacts to their normal positions, and notduring that portion of relay operation just described.

The closing of the contacts 205a and 205b connects the sensor drivemotor 169 across the power supply 180 so that it begins operation, whilethe opening of the contact 205c disconnects the resistor 209 from acrossits armature. The sensor drive motor 169 moves the sensor arm 160 awayfrom the sensor drive switch 167 and back to the retracted position ofFIG. 9, releasing the switch so that contact is made with the terminal167b instead of the terminal 167a. This causes the winding 205w to beenergized through conductors 181, 215 and 182, independent of thecontact 214b.

When the sensor arm 160 begins to retract, the sensor 22 is withdrawnfrom the area of the defect which it had sensed, so that its outputsignal terminates and the winding 214w of the sensor relay 214 is nolonger energized by the control module 220. This causes the contact 214ato close and the contact 214b to open. It is possible for the retractingmotion of the sensor 22 to permit the contact 214b to open before thesensor drive switch 167 has contacted the terminal 167b. Under thesecircumstances, the winding 205w would no longer be energized and thesensor drive motor 169 would become disconnected from the power supply180. To prevent this, a time delay is built into the relay 205 such thatthe contacts 205a and 205b remain closed, and the contact 205c remainsopen, a sufficient time to permit the mechanical switching of the sensordrive switch 167 to complete the holding circuit of the relay 205through the terminal 167b.

The sensor drive motor 169 continues to operate until the sensor arm 160has completed a full oscillation to the retracted position of FIG. 9 anda return to the operating position of FIG. 8, in which it contacts thesensor drive switch 167 once again. This causes the switch to disengagethe terminal 167b and again contact the terminal 167a. This deenergizesthe winding 205w and, after a short time delay, opens the contacts 205aand 205b to remove operating voltage from the sensor drive motor 169,and closes the contact 205c to connect the resistor 209 across thearmature to quickly stop the motor.

If, when the sensor returns to its operating position above the sawblade, it still detects the defect which previously caused it to producean error signal, the winding 214w of the sensor relay 214 will again beenergized, so that the time delay relay 205 will be energized throughthe contact 214b to continue operation of the sensor drive motor 169.This will occur repeatedly until, upon the return of the sensor 22 toits operating position over the saw blade, that defect is no longerdetected; but when this occurs, the resulting deenergization of therelays 214 and 205 terminates operation of the sensor drive motor 169,and energizes the winding 186w of the relay 186 through the contact 214ato renew operation of the carriage motor 32 and the saw blade drivemotor 35.

As can be seen in FIg. 17, The electrical condition of the carriagedirection-control relay 195 is independent of the relays and switchesutilized to control the starting and stopping of the motors 32, 35 and169. Therefore, the condition of the contacts of the reversing relay 195will be the same when the carriage motor 32 resumes operation as it waswhen it stopped for the correction of a defect.

OPERATION OF THE MACHINE

Overall operation of the tensioning and straightening machine 30 willnow be described. Before a saw blade 11 is mounted on the carriage 31,the relative positions of the various components of the machine must beadjusted to accommodate a saw blade of that particular diameter andthickness. If the center of a saw blade is always positionedsubstantially at the center of the carriage 31, then certain permanentadjustments may be made. The carriage 31 should be moved as far from thecarriage motor 32 as it is desired to travel. At that point, the limitswitch 60 may be permanently mounted to reverse the direction of travelof the carriage 31 in the manner previously described. With the carriageabutting the limit switch 60, the hammer 24 and anvil 25 are positionedso that the hammer may strike the saw very close to, but not at, itscenter, whose position is adjustably fixed by the center biasing means15, including the positioning bar 100 carrying the stud 101.

The sensor 22 should be directly over the anvil 25 when it is in itsoperating position; this can be adjusted by locating the sensor driveswitch mounting arm 166 so that the sensor arm 160 engages the sensordrive switch 167 when the sensor is aligned over the anvil. Theforegoing adjustments are independent of the dimensions of anyparticular saw.

The center stud 101 of the center biasing means 15 controls the positionof the center of the saw blade 11. Accordingly, it must be spaced adistance from the drive wheels 84 and 85 of the saw blade drive assembly34 which will permit the drive wheels to engage the saw blade at someoptimum distance from the edge of the saw. This distance differs fromblade to blade, depending on such variables as whether the saw blade istoothed or gulleted. By loosening the threaded fasteners 99, the metalblock 97 holding the positioning bar 100 of the center biasing means 15in place can be loosened so that the positioning bar 100 may be moved ineither direction to set the center stud 101 at the proper distance fromthe drive wheels 84 and 85. This can be done by linear measurement, orby actually placing a saw in position on the center stud 101. Thethreaded fasteners 99 should then be tightened.

By loosening the nuts 67 on the clamping bolts 66, the position of thewhole saw blade drive assembly 34 may be shifted along the carriage. Thesaw blade drive assembly should be moved to a position which places thecenter stud 101 at its desired location at the center of the carriage31. The nuts 67 are then tightened to lock the saw blade drive assembly34 in position. The extra length of the drive shaft 105 permits thisadjustment to be made without any need to move the saw blade drive motor35.

Referring to FIGS. 12 and 13, the height of the lower drive wheel 84 maybe adjusted by the spacer bolt 90 and draw bolt 91 so that the saw blade11 rests on it in a position producing the desired blade curvature andpermitting the blade to rest flat on the anvil 25 for proper hammeringwhen the blade is released by the lift assembly 115. The spacer bolt 92and nut 94 can then be adjusted so that the upper drive wheel 85 willproperly grip a saw blade of specified thickness against the drive wheel84, with a line between the centers of the two drive wheelsperpendicular to the surface of the saw blade.

By loosening the clamping bolts 117 and nuts 120, the saw blade liftassembly 115 may be moved to any desired position, the only requirementbeing the positioning of the lift screws 136 at a suitable distanceinward from the rim of the saw blade 11. This distance must take intoaccount the curvature needed for proper tensioning and straightening ofthe particular saw blade, but can readily be determined by those skilledin the art. The positions of the lift screws 136 and their heights mustbe such that the sensor will properly track, that is, will remain at afixed distance from, a correctly straightened and tensioned saw bladetraversed under the sensor by the carriage 31. Testing may beaccomplished by operating the machine with such a blade, omitting theuse of the hammer 24, and reading the output of the sensor 22 throughthe use of a system of flashing lights or the deflection of a meter todetermine how closely the surface of the saw blade is being tracked. Thelift screws 136 are adjusted until satisfactory tracking is achieved.Proper adjustment can be reconfirmed at any time by this method, usingas a standard a saw blade known to be properly tensioned andstraightened.

When mounting a saw blade on the carriage 31, the sensor arm 160 shouldpreferably be in the retracted position of FIG. 9, to prevent accidentaldamage to the sensor 22. Retraction of the sensor arm also actuates theair switch 172 to lower the lift screws 136 of the saw blade liftassembly 115 so that they do not interfere with blade mounting.

Loosening of the nut 94 of the saw blade drive assembly 34 lifts theupper drive wheel 85 and the center stud 101 so that the saw blade 11may be placed in position. The nut 94 is then tightened as far as itwill go; this is controlled by the previous adjustment of the spacerbolt 92.

With the saw blade thus secured in place, the carriage is moved toengage the limit switch 61, which is then positioned to set the limit oftravel of the carriage in that direction. This determines the outerradial limit of the area of the saw blade which will be sensed, and musttherefore be readjusted when blades of different diameters are to betreated.

The saw blade 11 is now properly mounted and operation of the tensioningand straightening machine may be begun by energizing the power supplies.The sensor arm 160 is moved from its retracted position by the sensordrive motor 169 to bring the sensor 22 to its operating position. Theair switch 172 is actuated by the sensor arm, causing the lift screws136 to dish the saw blade 11 and lift it from the anvil 25, as shown inFIG. 15. Continued motion of the sensor arm 160 brings it intoengagement with the sensor drive switch 167, stopping operation of thesensor drive motor 169 and starting the carriage motor 32 and saw bladedrive motor 35 as previously described.

The saw blade drive motor 35 causes the drive wheels 84 and 85 to rotatethe saw blade 11 around the center stud 101 at a constant speed, as thecarriage motor 32 reciprocates the carriage 31 between the limitswitches 60 and 61. This combined motion produces a relative motionbetween the sensor 22 and the saw blade 11 such that the sensor traces ahelical path over substantially the entire bowed surface of the sawblade, within the radial limits established by the positions of thelimit switches.

The curvature of the bowed saw blade and the opposed curvature of thepath of the carriage, shown by the arrow 51 in FIG. 10, combine tomaintain the surface of a properly-tensioned saw blade at asubstantially constant distance from the sensor 22. If at any point inthe sensing operation a portion of the surface of the saw bladeapproaches closer to the proximity sensor 22 than the predetermineddistance, this will be detected. The resulting signal produces theswitching operation described in connection with FIG. 17, whichimmediately stops operation of the carriage motor 32 and the saw bladedrive motor 35, promptly halting the saw blade with the sensed defectpositioned over the anvil 25. Operation of the sensor drive motor 169 isbegun by the sensor signal, and is maintained by the consequent releaseof the sensor drive switch 167 by the sensor arm 160. As the sensor arm160 retracts outwardly, it releases the air switch 172 so that the sawblade 11 is lowered onto the anvil 25. Upon reaching the limit of theretracting motion, the camming plate 174 on the sensor arm 160 engagesthe air switch 175, causing the hammer to sharply strike the defect inthe saw blade.

The sensor arm 160 then returns toward its operating position over thesaw blade 11, and the air switch 175 is released so that the hammer 24is raised to its rest position. The sensor arm 160 again engages the airswitch 172, which causes the saw blade to be lifted into its bowedconfiguration again. During the further interval of travel of the sensorarm 160, any vibrations in the saw blade 11 are damped out. The motionof the sensor arm continues until it re-engages the sensor drive switch167. If the originally-sensed defect is still present, the sensor drivemotor 169 will continue to operate and the hammering cycle will berepeated. When the defect is no longer present, the sensor's drive motorstops operating when it engages the sensor drive switch 167, thecarriage motor 32 and saw blade drive motor 35 begin operating again,and the sensing of the saw blade surface resumes.

When tensioning and straightening of one side of the saw blade has beencompleted, the sensor arm 160 is retracted from the saw blade to lowerthe lift screws 136, and the nut 94 is loosened so that the saw blademay be removed. The saw blade is then turned over and the processrepeated. The saw blade should then be properly straightened andtensioned and ready for use. It may, however, be desirable with certainsaws, such as highly defective ones, to operate on both surfaces of theblade two or three times, depending upon the extent of defectiveness andthe degree of straightening which is desired.

THE MACHINE - SECOND EMBODIMENT

An alternative embodiment 300 of the tensioning and straighteningmachine of this invention is illustrated in FIGS. 18 and 19. Thisembodiment is exemplary of the use of movement of the sensor to aid insweeping it over the blade surface. In the previously describedembodiment, only the saw blade was moved during sensing, while thesensor remained stationary.

This embodiment of the tensioning and straightening machine 300comprises a base 301 on which is mounted an oscillating table 302 drivenby a motor (not shown), and includes limit switch means for reversingthe direction of operation of the motor to produce limited arcuatemovement of the table about a vertical axis, back and forth between thepositions of the limit switches. The arc length of this oscillatingmovement does not exceed the radius of the saw blade to be treated, forreasons which will shortly appear.

In this embodiment a hammer 304, anvil 305 and sensor 306 are mounted onthe table 302 for oscillatory movement therewith, while the center ofthe saw blade 307 is held fixed with respect to the base 301. As in thefirst embodiment, the saw blade is supported by a saw blade driveassembly 309, which is substantially identical to the drive assembly 34of the first embodiment and is schematically represented in FIG. 18 byan upper drive wheel 310 and a lower drive wheel 311. Also supportingthe saw blade 307 is a fixed saw blade lift assembly 312 having a pairof lift screws 314. Both the drive assembly 309 and the lift assembly312 are mounted on the base 301 independent of the oscillating table302. A center-biasing means 315 is also mounted on the base 301, and hasa center stud 316 for locating and dishing the saw blade 307 in themanner previously described.

The lift assembly 312 is substantially similar in structure andoperation to the lift assembly 115 of the embodiment illustrated inFIGS. 14-16, and is operated by an air actuator 317. The center-biasingmeans 315 is adjusted independently of the saw blade drive assembly 309,and is separately operated by an air actuator 319.

With the center of the saw blade 307 held in a fixed position withrespect to the base 301 while the blade is rotated around the centerstud 316, the preferred helical path of sweeping the sensor across theblade is attained by moving the sensor 306 itself. The anvil 305, hammer304 and sensor 306 move together with respect to the saw blade 307, allbeing mounted on the oscillating table 302; the oscillating motion ofthese elements is in arcuate paths determined by their distance from thecenter of the table 302, and of an arc length determined by thelocations of the aforementioned limit switch means. The anvil 305 ismounted on the table in a position beneath the sensor 306, and thehammer 304 is supported above the anvil by mounting legs 320 and a shaft321. A striker block 322 is operable by an air cylinder 324 to strike ashaft 325 of the hammer 304 to impact it against the saw blade.

A sensor mount assembly 326 best shown in FIG. 19 comprises a base 327,which is positioned at the center of the oscillating table 302 but isfixedly mounted on the base 301 and does not turn with the table. Asocket 329 is formed in the center of an upper surface 327a of the base327 to accommodate a ball 330. A corresponding socket (not shown) isformed in the lower surface of an adjusting plate 331 to receive theball 330. The adjusting plate 331 is attached to the base 327 by aplurality of screws 332 which may be, for example, four in number. Theball 330 is sufficiently large in relation to its sockets that it spacesthe base 327 and adjusting plate 331 a predetermined distance apart whenthey are secured together by the screws 332.

A sensor arm mounting block 334 is secured to the adjusting plate 331 bya screw 335. A sensor arm assembly 336, to which is attached the sensor306, is pivotally mounted on centering screws 337 between the adjustingplate 331 and the mounting block 334 so that the pivotal axis of theassembly 336 extends directly above the ball 330 which, in turn, ispositioned at the center of the oscillating table 302.

A sensor drive rod 339 is connected between the sensor arm assembly 336and a crank 340. The crank 340 is mounted on a sensor drive motor 341for the purpose of moving the sensor with respect to the oscillatingtable 302, between a position retracted from the saw blade for hammeringoperations, and the operating or sensing position over the blade whichis illustrated in the drawing.

The saw blade is rotated around the center stud 316 by the saw bladedrive assembly 309. No lateral motion of the saw blade is provided for.The sensor 306, hammer 304, and anvil 305 are caused to oscillate overthe surface of the blade by the motion of the motor-driven oscillatingtable 302, which moves back and forth arcuately between terminalpositions established by the locations of a pair of limit switches (notshown), as previously described. These locations are adjusted so thatthe sensor sweeps back and forth between one terminal position close tothe stud 316 at the center of the blade, and another near but radiallyinside the cutting edge and any gullets which may be provided in it.Because the sensor oscillates in an arc having a relatively largeradius, substantially that of the table 302, its path approximates alinear radius of the saw blade.

The saw blade to be treated is bowed toward a predetermined curvature byan upward bias applied by the lower drive wheel 311 and the lift screws314, in combination with a downward bias applied by the center stud 316.The structure of the sensor mount assembly 326 is such that theoscillating motion of the sensor 306 can be given the same curvature asthe blade in planes parallel to the axis of rotation of the blade, i.e.normal to the surface of the undeflected blade, so that the sensor ismaintained at a uniform distance from the locus of predeterminedcurvature of the bowed blade throughout its sweeping movements, and istherefore enabled to detect deviations of the blade surface from thisideal locus correctly. Since the base 327 is fixed in position withrespect to the base 301, the adjusting plate 331 and sensor arm mountingblock 334 are also fixed in position. As the table 302 oscillates, thesensor drive rod 339, connected to the table through the now-stationarysensor drive motor 341 and crank 340, oscillates the sensor arm assembly336 arcuately about an axis defined by the centering screws 337. If thecentering screws 337 are vertically aligned with each other, the sensor306 sweeps through an arc on which all points are at a constant distancefrom the table 302. However, by adjusting the screws 332, the adjustingplate 331 can be tilted over the ball 330 to form any of a variety ofangles with the base 327. The arcuate motion of the sensor can thus bein a plane inclined to the table, with a result substantially similar tothat provided by the tilted carriage 31 of the tensioning andstraightening machine 30 previously described, i.e. that the sensorremains at a uniform distance from the locus of the curved plane orcylindrical segment in which the saw blade surface should ideally lie.In addition to providing for curved relative vertical motion, thetwo-directional adjustability of the adjusting plate 331 with respect tothe ball 330 provides sufficient versatility of curvature to avoid anyneed for fine adjustment of the relative heights of the lift screws 314.

The hammer 304 and anvil 305 oscillate with the sensor 306 and the table302, and so are always in position to hammer that part of the saw bladebeing sensed. Should a defect be detected, the motions of theoscillating table 302 and saw blade drive assembly 309 are stopped, thelift screws 314 are lowered from the blade 307, and the motor 341 isoperated to retract the sensor 306 from its operating position above thedefect. The defective area of the blade is then struck by the hammer304. The sequence of operations may be controlled by suitable switches(not shown), operated for example by cams rotating with the crank 340.

VARIATIONS

Various modifications may readily be made; for example, thestraightening and tensioning machine and method can be adapted for useon band saw blades.

The sensor 22 may be any of a number of known types capable ofaccurately detecting minute variations in the location of a small areaof the blade, though I presently prefer to use a device which isresponsive to variations in electromagnetic inductance across an air gapbetween the sensor and the blade. A photocell device responsive toreflectivity, or a mechanical feeler gauge, are subject to thepossibility of inaccuracy caused by surface roughness or foreign matteron the blade surface. The same may be true of a pneumatic sensorresponsive to a pressure drop through a gap between an orifice and theblade surface.

While the improved method has been described as it may be practiced inseveral automatic embodiments of my improved machine, it may also bepracticed manually with the aid of appropriate equipment, including afixture for supporting the blade and bowing it toward a predeterminedcurved surface, and a device for supporting a suitable sensor; theseelements being relatively movable for sweeping the sensor over the bladesurface, while maintaining a uniform distance between the sensor and thecurved surface. In practicing the method manually it is not essential,although desirable, to maintain a hammer in alignment with the sensor,or to hammer each defect as it is detected before continuing thesensing, to eliminate the need for marking the locations of defects.Thus in its broader aspects, the method may include manual hammering. Inapplications requiring only a modest rate of production, this manualpractice of the invention may be carried on by relatively unskilledpersons, as it is only necessary to sweep the sensor over the surface,to mark the location of any defects which it may indicate, and then tohammer them, so that very little judgment is required.

In preferred embodiments and modes of practice of the invention, the sawblade is bowed elastically around an axis parallel to its diameter, tolie in a curved plane which is a segment of a cylinder that is notordinarily of a circular cross section. However, the blade might be bentinto the form of a segment of an oblate spheroid, such as an ellipsoidor the like; the sensor would then be swept through a parallelsimilarly-curved surface. In more general terms, it may be stated thatthe saw blade is elastically deflected toward the locus of a segment ofthe surface of any selected curved geometric solid having apredetermined contour, in which locus the blade surface would lie if theblade is correctly straightened and tensioned.

In the case where the sensor is physically moved to sweep the bladesurface, as opposed to remaining stationary while the blade isphysically moved, the sensor can then be swept through a segment of thelocus of a second geometric solid which is congruent with, parallel to,and uniformly spaced from the first, thereby maintaining the sensor at auniform distance from the desired locus of the blade surface. But in thecase where the sensor is held stationary, the blade is physically movedin a manner to maintain all points of the locus of its ideal curvatureat a uniform distance from the sensor.

The convex surface of the bowed saw blade may optionally be inspectedfor tight spots, which appear on this surface as areas that are flatterthan the proper contour, by reversing the sensor to respond to surfaceareas that are farther from the sensor than the standard distance.However, it is more facile to sense the concave surface, as in theillustrated embodiments.

Another option is to use a sensor which responds to, and discriminatesbetween, displacements by the hammer of the blade surface toward or awayfrom the sensor. Situations may arise, such as when the impact is spreadover an enlarged area by a worn hammer and anvil, the blade does not lieflat on the anvil, the blow is misaligned, or the blade is too thick forthe weight and velocity given to the hammer, in which hammering maymerely peen the surface and fail to permanently deform the blade clearthrough. Since peening spreads the surface, the result may be that thedefect is raised rather than reduced. Detecting this occurrence permitsimmediate correction. In the case of a saw that is very thick, theopposite surface may be peened to offset this effect by relieving thestress, or the hammer may be given an appropriately-heavier mass orincreased velocity.

I claim:
 1. A machine for locating variations in tension in a saw blade,said machine comprising:carriage means constructed and arranged formounting and elastically bowing a saw blade having a normally-planarmajor surface to deflect said surface toward the locus of a segment ofthe surface of a curved geometric solid having a specificallypreselected contour, to which said blade surface would conform if theblade is properly tensioned and straightened; sensor means constructedand arranged for response to variations in its distance from the nearestarea of said blade surface; and means constructed and arranged forsupporting said sensor means and said carriage means for relativemovement of said sensor means with respect to said curved locus at apredetermined substantially uniform distance therefrom; said sensormeans being operatively connected to produce a signal only in responseto a substantial variation in its distance from said blade surfaceoccasioned by a local deviation of said blade surface from said curvedlocus.
 2. A machine as recited in claim 1, together withselectively-operable motive means drivingly connected with saidsupporting means to produce said relative movement, and operativelyconnected for control by said sensor means to produce said relativemovement in the absence of a signal from said sensor means, and todiscontinue said relative movement upon production of a signal by saidsensor means to permit corrective action to be taken immediately uponsensing of a local deviation of said blade surface from said curvedlocus.
 3. A machine for locating variations in tension in a circular sawblade having a major axis, said machine comprising:carriage meansconstructed and arranged for mounting and elastically bowing a saw bladehaving a normally-planar major surface to deflect said surface towardthe locus of a segment of the surface of a curved geometric solid havinga specifically preselected contour, to which said blade surface wouldconform if the blade is properly tensioned and straightened; sensormeans constructed and arranged for detecting local deviations of saidblade surface from said locus only in a limited local area of the bladesurface at a time; and means supporting said sensor means and saidcarriage means in operative relation for detection of said localdeviations by said sensor means, said supporting means being constructedand arranged to support said carriage means and said sensor means forrelative reciprocatory movement therebetween, and including means forrotating said saw blade about said major axis, to cause said sensormeans to locate said local deviations in a larger area of said bladesurface sequentially.
 4. A machine as recited in claim 3, in which saidsupporting means are constructed and arranged to limit the relativereciprocatory movement between said carriage means and said sensormeans, in a plane normal to said major axis of the saw blade, to a pathlength not exceeding the radius of the saw blade.
 5. A machine asrecited in claim 3, in which said supporting means are constructed andarranged: for relative reciprocation of said carriage means and saidsensor means in directions having components both parallel to saidnormally-planar major surface of the mounted saw blade when undeflected,and normal thereto; and for controlling the latter component of relativereciprocation in direction and amount to maintain said sensor means at auniform distance from said locus.
 6. A machine as recited in claim 5, inwhich said supporting means comprise: a pair of parallel arms pivotallyconnected with said carriage; and means pivotally supporting said armsfor angular movement of said carriage about parallel axes inclined tosaid normally-planar major surface of the mounted saw blade whenundeflected.
 7. A machine as recited in claim 5, in which saidsupporting means comprise: table means mounted for oscillatory movementabout an axis normal to said normally-planar major surface of themounted saw blade when undeflected; sensor-mounting means supportingsaid sensor means for oscillatory movement about an axis inclined tosaid major surface when undeflected; and means interconnecting saidsensor-mounting means and said table means to produce oscillatorymovement of said sensor means about said inclined axis as said tablemeans is oscillated about said normal axis.
 8. A machine as recited inclaim 3, said supporting means positioning said sensor means at auniform distance from said locus, said sensor means being responsive todeviations in the distance between said blade surface and said sensormeans from said uniform distance.
 9. A machine as recited in claim 8,said sensor means being responsive only to decreases in the distancebetween said blade surface and said sensor means to values less thansaid uniform distance, said deflected surface of the saw blade having aconcave curvature, and said supporting means positioning said sensormeans to confront said concave deflected surface for response toprotrusions therefrom.
 10. A method of locating variations in tension ina saw blade having a normally-planar surface, comprising the steps ofelastically bowing the blade to cause said surface thereof to deflecttoward the locus of a segment of the surface of a curved geometric solidhaving a specifically preselected contour, to which said blade surfacewould conform if the blade is properly tensioned andstraightened;selecting sensor means responsive to produce a signal onlyin response to a substantial variation in its distance from the nearestarea of said blade surface; and moving said sensor means relative tosaid curved locus at a predetermined substantially uniform distancetherefrom, to detect local deviations of said blade surface from saidcurved locus.
 11. A method as recited in claim 10, in which the step ofrelatively moving said sensor means is discontinued upon production of asignal thereby, to permit corrective action to be taken immediately uponsensing of a local deviation of said blade surface from said curvedlocus.